1. Field
Embodiments of the present invention generally relate to a method and apparatus for fabricating a semiconductor device.
2. Description of the Related Art
Hardmasks are used to fabricate NAND and dynamic random access memory (DRAM) devices. Hardmasks are commonly used as sacrificial layers in lithographic patterning and enable, through an etching process, the patterning of features onto a layer of a semiconductor device. The patterned features can form, for example, the transistors and interconnects that allow the NAND and DRAM devices to operate.
The important properties of a hardmask material are etch resistance, compressive stress, mechanical properties, and removability. An ideal hardmask has a high etch resistance compared to the layer to be etch (hereinafter, an “underlayer”) so that the underlayer etches in an etch process whereas the hardmask does not. A high etch resistance allows efficient transfer of the pattern of the hard mask to the underlayer. Etch resistance generally shows a positive correlation with hardmask density. An ideal hardmask also has a low compressive stress. A lower compressive stress eliminates undesirable wafer bow after hardmask deposition. Wafer bow can make further device fabrication difficult. In addition, an ideal hardmask has strong mechanical properties. For example, a high Young's modulus or hardness will reduce the line bending of high aspect ratio structures after a mask open step. Finally, an ideal hardmask is easily removed to simplify the fabrication process.
Current hardmasks are insufficient for developing next generation NAND and DRAM devices. As the feature sizes of NAND and DRAM devices decrease, etch selectivity and ease of removal need to increase while compressive stress needs to decrease. However, attempts at increasing etch selectivity have resulted in an increase in compressive stress, and attempts at decreasing compressive stress have resulted in a decrease in etch selectivity. For example, carbon-containing hardmasks with a high C:H ratio exhibit a good etch selectivity, but the materials have very high compressive stress.
Therefore, there is a need in the art for a hardmask having a high etch selectivity and a low compressive stress.